If treatment is available for one dementia and not another, patients and caregivers yearn for diagnostic certainty, because obtaining definitive answers can alter the length and quality of their lives. However, when patients over age 70 present with symptoms of frontotemporal dementia - personality change and behavioral disturbance - along with the early memory loss associated with Alzheimer's Disease, diagnosis can remain elusive, leaving doctors, patients and families uncertain of the appropriate course of action. Clinician-Scientists at the University of Toronto want to change this. Disease-modifying agents for Alzheimer's disease (AD) will likely be available sooner than for those with frontotemporal dementia (FTD). The beta-amyloid radiotracer - a neuroimaging technique that detects the presence of abnormal amyloid collections in the brain and therefore enhances diagnostic assurance - is one of the most promising developments of this decade. This study would use amyloid PET imaging of the brain to determine if cases of late-onset FTD bear AD pathology. It also will help clinicians understand if there is a role for future anti-amyloid interventions in the treatment of frontotemporal dementias. The proposed analysis draws on the strength of collaboration among investigators from the Rotman Research Institute, who have a proven track record in clinical research on FTD, and the Centre for Addiction and Mental Health's Geriatric Mental Health Program and PET Imaging Centre. If funding is received, CAMH will provide scanning for half of the sample of subjects, thus increasing the value of the grant and completing the proposed protocol.